Transformer

Yes you can....

http://www.allaboutcircuits.com/vol_2/chpt_9/2.html

Yes but unless you really know what is going on it is not recommended. Stepping up a voltage without knowing the breakdown voltage of everything on the high voltage side can release smoke.

It actually depends upon the applied voltage I am pretty sure. If a 120 to 12 volt VAC (Nominal) transformer is connected "backwards" to 12 VAC, that should work fine. If not, it was crap quality.

In fact I would assume that the insulation will probably be OK up to say 24VAC being attached to the secondary.....just a guess.

But if the input on the 12 VAC side is say 120VAC, then someone may get a big problem.....it may or may not be OK.....depending upon quality of insulation......

I have never tried it exactly, but many years ago I made electronic ignitions using a 220 to 12 VAC transformer (backwards!) feeding an ignition coil with a high enough voltage that if things were not kept clean, voltage sparked all over the place on the low voltage side of the coil as well.....a good clean and a good ignition spray were needed....

We (I was not the only one making and attaching them to cars) did two things to be safe:-

1) Big warning notice NOT to work on the engine with the transistor ignition enabled as High Voltage was present. A Neon glowing/showing if high voltage was present.

2) Big switch to return all to "normal" operation (still painful if touched!) when working under the hood.

I never ever had a failure of the transformer or the ignition coil. The units even helped on worn engines that were burning oil and gumming up the plugs before the TI was installed.....the higher voltage kept the plugs clean all the time.

This was around 1973.

I hope this in some way explains my personal take on what you said.....

"But if the input on the 12 VAC side is say 120VAC, then someone may get a big problem.....it may or may not be OK"

Andy -
If you connect a winding designed for 12 VAC operation to a power source supplying 120 VAC, then be sure to have a fire extinguisher ready! Doing so will cause saturation, over heating then fire! The designed current carrying capacity of the magnet wire and number of turns on that winding is not enough and sufficient to safely handle such!

The designed power handling capacity of the transformer comes into the picture, as it determines the AWG size of copper + size of the core area where it is wound in any given transformer!

You obviously did not read the post I was replying to.....Redfred I believe....

I also believe that I implied that attaching 120VAC to the 12v secondary, was probably a bad idea.....it hangs with the quality and degree of insulation and the wire size used.....can you be certain or not that every transformer will fail.....I cannot as I have not tested ALL of them.

I would expect (as I posted) that double voltage would probably work. Do you have any argument with that?

Why did you post at all?

Yes, just reverse it, when it's simple single tap transformer. Be careful if its multi-tap as per RedFred

Yes. It is feasible because you're supposed not to exceed the rated KVA of the transformer.

If the voltages used in the new step-up configuration are the same as the old step down configuration, just reversed connections, there is no problems since both windings have sufficient insulation to handle the original voltages.

If either winding's voltage is higher then further investigation of documentation/research must be done to confirm that the insulations are rated high enough to handle the higher voltages. Best source would be the spec sheet or call the manufacturer.

If both voltages are lower than the original set up, no problems involved.

Why? The voltage on a winding can not exceed the insulation rating of the winding. If it is exceeded it probably will break down and short out the winding. It is also possible to cause a break in the winding wire. Neither of which is a "happy time".

Good Luck, Old Salt

Yes Mr. Kumar,

You can use step down transformer as step up transformer, provided AMPERE-TURN ratio and Insulation aspect is taken care.

Care to be taken that stepped up volltage does not exceed the Voltage prescribed value.

In other words, the Voltage meant for step down should not be connected to LV side, which will step up and cause problem by way of insulation failure, short circuit, flashing/arcing/bursting etc.

DHAYANANDHAN.S

thank u all

To watch for...

Very often a step down secondary winding has a center tap used for the secondary neutral. This tap is often bonded to ground and to the case of the transformer. Make sure YOU REMOVE any such connections before you flip the transformer.

Yes you may....

As long as the designed T/V ratio is considered or strictly observe together with its rated capacity since power transform remains the same.....

If you apply excessive voltage to the new primary, you may saturate the core and draw excessive primary current. Stay within the voltage rating and you may draw a little extra current only, and yes it will work OK.

Keep in mind that the internal loss in the transformer will cause a reduction of the output voltage.

A transformer designed for down transforming 400V to 230 V, used in a 230V supply system to boost up the voltage will only give +/- 380 V output at full load.